In response to partial outlet obstruction, the urinary bladder is capable of undergoing hypertrophy via a complex remodeling process that allows it to adapt to its new workload. This remodeling is driven by a number of signaling cascades and their corresponding transcription factors. This proposal focuses on the role of the calcineurin pathway and its associated transcription factors the Nuclear Factor of Activated T Cells (NFAT) and Myocyte Enhancing Factor 2 (MEF-2). Preliminary data support our central hypothesis that partial bladder outlet obstruction is associated with dysregulation of intracellular calcium homeostasis and activation of calcineurin and the subsequent nuclear importation of NFAT. With administration of cyclosporine A (CSA), the resulting bladder hypertrophy is diminished, and there is a reversal of the myosin heavy chain (MHC) mRNA isoforms back towards a normal expression pattern. We propose to further study these observations in a murine model of partial bladder outlet obstruction using a transgenic mouse containing an NFAT-luciferase reporter construct in the presence and absence of CSA administered of varying time points. End points will include bladder mass, in vitro determinations of contractility and shortening velocity, morphology, and a molecular analysis of MHC isoform expression. We also seek to localize in situ, which bladder wall cell population(s) show evidence of calcineurin activation. We also seek to localize the sites where DNA synthesis is taking place within the bladder wall and determine whether these sites of DNA synthesis represent fibroblasts, smooth muscle cells, or both. These in vivo experiments are complemented by in vitro experiments using cultured cells to assess the impact of mechanical deformation upon NFAT and MEF- 2 translocation to the nucleus. This approach will allow for in vitro screening of compounds that can prevent calcineurin activation, and will allow for study of the interaction between NFAT, MEF-2 and the smooth muscle MHC promoter. Using microarray methods we propose to identify the NFAT and MEF-2 responsive target genes within two cell populations;bladder smooth muscle and bladder fibroblasts. The relevance of this proposed work to human disease is apparent when one considers the socially devastating sequelae of urinary incontinence and renal failure that may result from untreated bladder wall hypertrophy. PUBLIC HEALTH RELEVANCE: Human Relevance - Two conditions can result in severe bladder wall hypertrophy in children, posterior urethral valves, and spinal bifida. If left untreated bladder wall hypertrophy leads to the socially devastating sequelae of urinary incontinence and in extreme cases renal failure may result as the bladder loses its ability to store urine at low pressures. New therapy to preserve and enhance native bladder function will help avoid the development of the end stage bladder.